Why does middle c on an oboe sound different then a middle c played on a piano

Because an oboe has a low sound and an middle c is much higher note

Answer: Flutes, oboes, bassoons, trombones, tubas, baritones reading bass clef and all string instruments are concert pitch instruments: when they play a C it sounds like a C on the piano. They don't have to transpose. (All instruments that mostly read bass clef are in C, but some - like bass guitar and string bass - are written an octave higher to keep the music in the staff).

Explanation: Pitch is off